This relates generally to imaging systems, and more particularly, to imaging systems with clear image pixels.
Image sensors are commonly used in electronic devices such as cellular telephones, cameras, and computers to capture images. In a typical arrangement, an electronic device is provided with an array of image pixels. The image pixels generate image signals in multiple color channels. Readout circuitry such as analog-to-digital converter circuits are commonly coupled to the image pixels for reading out image signals from the image pixels.
During image rendering, image signals generated by the array of image pixels may be subject to clipping at low light levels. Such clipping can undesirably modify the image signals and can cause nonlinear response in the image sensor. Image pixels may also be subject to undesirable dark current. If care is not taken, dark current removal and clipping can cause irreparable image artifacts in the final image produced by the image sensor.
In conventional imaging systems, a single black offset value is uniformly added to image signals generated by the image pixels in all color channels and dark current is ideally subtracted from the image signals prior to passing the image signals to the analog-to-digital converter circuits. However, image signal clipping can persist for some of the color channels when a single black offset value is uniformly added for all of the color channels and when dark current and all added offsets are subtracted from the image signals prior to denoising the image signals.
It would therefore be desirable to be able to provide imaging systems with improved image signal clipping mitigation capabilities.